290 



as the HO-group formerly occupied, the respective substitution- 

 products could yet have oppositely directed rotations. 



Moreover, in replacing halogen-atoms by hydroxyl-groups, the 

 remarkable difference between the action of Ag 2 and KOH, as 

 already stated above, has been repeatedly observed. According to 

 Biilman 1 ) this difference of action is intimately connected with 

 the fact, that the reaction with silver-compounds goes on very 

 rapidly, while that with potassium-hydroxide on the contrary very 

 slowly. The rapid change would occur without a change of con- 

 figuration, the slow one with a rearrangement of the atoms in space. 

 Mercuric oxide also seems to act upon halogenated acids in the 

 same way as silver-oxide. 



The change of an amino-3.cid into an hydroxy-acid by means 

 of nitrous acid, is a very quick reaction ; therefore, no change of 

 configuration would take place here, and Biilmann concludes, 

 that the aspartic acid and the malic acid in plants would have 

 the same spatial arrangement of the groups placed round the 

 asymmetric carbon-atom. 



4. But here we touch the crucial point of the problem under 

 consideration: for how can we be sure whether the original asym- 

 metrical configuration has been changed during the process or not ? 

 If the reactions without change of configuration be named normal, 

 and those accompanied by such a change abnormal substitutions, 

 we may ask: when must a chemical reaction be considered as a 

 -normal and when as an abnormal one? 



The answer to this question has occupied a number of chemists, 

 because it is evidently closely related to the particular views on 

 the mechanism of substitution in such asymmetric molecules, and 

 several explanations of the Wai den-in version have been suggested 

 by various authors. 2 ) 



Some of them, especially Armstrong, Gadamer, and 



1 ) E. Biilmann Ann. der Chemie, 338, 335, (1911). 



2 ) H. E. Armstrong, Journ. Chem. Soc. London, 69, 838, 1399, (1896); E. 

 Fischer, Berl. Ber., 40, 492, (1907); Ann. der Chemie, 381,312, (1911) 386,374, 

 (1911); 394, 352, (1911); J. Gadamer, Chem. Zeitg., 34, 1004, (1910); 36, 1327, 

 (1912); J. A. Le Bel, Journal de Chim. phys., 9, 323, (1911); A. Werner, Ber. 

 d. d. Chem. Ges., 44, 873, (1911). E. Biilmann, loco cit.; P. F. Frankland, 

 loco cit., p. 738; cf. also: G. Senter, Journ. Chem. Soc. London, 107, 638, 

 (1915); 109, 1091, (1916); S. Arrhenius, Theorien der Chemie, 2e Aufl., (1909), 

 p. 83; E. Mohr, Chem. Zeitg., 36, 984, 1912); P. Pfeiffer, Lieb. Ann., 383, 

 \23, (1911). 



